Drive units for motor vehicles of the type mentioned above are, for instance, proposed by DE 10 2005 061 078 A1, DE 103 08 700 A1, and DE 103 08 698 A1. Special designs of the so-called twin clutches for application with such drive units are, for instance, proposed by DE 102 38 403 A1, DE 34 46 460 C2, DE 100 64 459 A1, DE 100 13 576 A1 and DE 101 55 458 A1. Basically, both types of twin clutches are known, whereby both clutches are closed from outside by forces applied forcibly to the actuating means of the clutches as well as twin clutches by which the clutches feature a separate energy accumulator, e.g. a diaphragm spring that at least partially applies the contact force required for closing the friction clutch. The latter clutches involve the so-called closing clutches, whereas by the clutches that are closed mainly by means of force applied from outside are called automatically opening clutches. Also embodiments of a twin clutch are possible, in which a closing as well as an automatically opening friction clutch is available.
Only the automatically opening clutches have prevailed in practice, in particular when the so-called dry clutches are used in connection with a power shift gearbox. This design is necessary to ensure that both clutches will open in the event of a malfunction in the activation system of the power shift gearbox and/or at least in the event of a malfunction in one of the two friction clutches. Thereby, damage to the drive train can be avoided, in particular in the gearbox, for instance, because of a blocking effect when both friction clutches are closed. The reasons for such malfunctions within the control device and the actuators controlled by this control device are, for example, power failures that interrupt the hydraulic and/or pneumatic and/or electric power supply to the respective actuators. A cause of power failure, for instance, can be a fallen connector or failure of a circuit breaker. To avoid critical driving situations, automatically opening friction clutches have been used as already mentioned above. These clutches open automatically in the event of certain operational malfunctions.